This invention relates to the stabilization and preparation of foamed polyvinylchoride resins. In particular this invention relates to the use of stabilizers for foamed polyvinylchloride resins as activators for the blowing agents used in the preparation of foamed polyvinylchloride resin. An important aspect of this invention is the use of organotin compounds as the thermal stabilizer and activator for the blowing agent in the preparation of rigid foamed polyvinylchloride products.
It is well established that organotin stabilizers are effective for the thermal stabilization of polyvinylchloride resins. U.S. Pat. Nos. 2,597,920 to Carroll and 2,763,632 to Johnson disclose reaction products of diorganotin oxides and esters of diorganotin oxides as heat and light stabilizers for vinylchloride resins. Despite their high tin content, these reaction products are rather poor in stabilizing effectiveness.
Among the effective organotin stabilizers for inhibiting the polyvinylchloride resins at high temperatures are the organotin mercapto acid esters. Patents disclosing the use of these compounds include U.S. Pat. Nos. 2,641,588 and 2,641,596 to Leistner et al; U.S. Pat. No. 2,648,650 to Weinberg and U.S. Pat. No. 2,890,956 to Mack et al.
The dialkyltin bis-alkylthioglycolates, alone and in combination with other components, have been widely accepted for various commercial applications. Among the combinations reported including the dialkyltin bis-alkyl thioglycolates as a component are U.S. Pat. No. 2,914,506 to Mack et al disclosing combinations of organotin thioglycolates with compounds such as metal salts, epoxy compounds, phosphates and phenols and U.S. Pat. No. 3,640,953 to Brecker et al disclosing combinations of diorganotin mercaptocarboxylic acid esters and a diorganotin-ester complex which is a reaction product of a diorganotin oxide and an ester of an oxygen-containing acid. The compounds of Brecker et al have particularly been found to be highly efficient in the heat stabilization of polyvinylchloride.
One important utility for polyvinylchloride resins is in the preparation of rigid foamed articles. The articles are ordinarily manufactured by known methods, for example by extrusion, by blending the plastics material with a suitable blowing agent and choosing the processing temperature such that it is above the decomposition temperature of the blowing agent. Often, however, the decomposition temperature is too high above the processing temperature, so that the blowing agent cannot be used alone. For this reason, activators are often employed which hasten the decomposition of the blowing agent and/or lower the decomposition temperature.
In the search for effective activators, the use of compounds that are also effective thermal stabilizers has become a highly desirable possibility in order to reduce the number of components of the resin blend. Organotin oxides, organotin alcoholates and mixtures thereof have been described in the literature as being useful as activators. U.S. Pat. No. 4,698,368 to Muller discloses mixtures of organotin mercaptides as imparting good light and heat stability and as being effective activators for the manufacture of foamed plastics. These mixtures can optionally contain an organotin carboxylate. Also disclosed in this patent as being useful as light and heat stabilizers and as activators are mixtures of organotin mercaptides and organotin carboxylates.
Also U.S. Pat. No. 3,706,679 to Hopton et al discloses a mixture of organotin thioglycolate, particularly di n-butyltin bis(isoctylmercaptoacetate) and barium salts of saturated fatty acids having from 14 to 18 carbon atoms, such as barium stearate or palmitate.
Yet despite the foregoing disclosures, there is present a need for additional activators for the preparation of polyvinylchloride resins that also afford effective thermal stabilization of the foamed polyvinyl resin.
It is therefore an object of the present invention to provide effective activators for the preparation of rigid foamed polyvinylchloride articles.
Another object of the present invention is to prevent the discoloration of foamed polyvinylchloride articles during their manufacture.
Another object of the present invention is to provide compounds useful as thermal stabilizers and activators for the normal blowing agents useful in foaming polyvinylchloride resins.
Still another object of the present invention is the formation of rigid polyvinyl articles utilizing the blowing agents and thermal stabilizers that are acceptable commercially.